Abu Rayhan al-Biruni · Science
Al-Biruni’s celebrated dip-angle method at the fort of Nandana: with one hill of known height, an astrolabe, and a little trigonometry, a single observer standing in one place computed the radius of the whole earth - and measurement, for him, was the beating heart of science.
You learned that at Nandana al-Biruni measured the height of a hill and the small angle by which the horizon dips when seen from its summit, then used trigonometry to compute the earth’s radius from a single spot. Explain how the method works, and why the accuracy of his result depends on how long his ‘cub…
Leads to Eratosthenes.
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